In known thread clamping devices the knotter needle serves for drawing the two thread ends into the interior of the knotter mandrel during the end phase of the knotting operation and for holding said ends in said interior until the knot is tightened. To this end, it is known to impart a predetermined curvature to the front end of the knotter needle consisting of a resilient material so that the hook of the knotter needle is pressed under tension laterally in engagement with the inner wall of the knotter mandrel. Whilst the knotter needle is retracted into the knotter mandrel, the thread ends of the thread to be knotted then extend through between the needle hook and the inner wall of the knotter mandrel.
They are pressed-on in engagement with the inner wall of the knotter mandrel by the tension of the knotter needle so that a sufficiently great counter-tension for tightening the knot is produced in the thread ends. Yet when the knot is tightened then the thread ends must be completely drawn out from the knotter mandrel. At the same time, the hook of the knotter needle is firmly clamping the thread ends now as before. In known knotting devices the adjustment of the tension with which the hook of the knotter needle presses onto the thread ends is very difficult because this tension is, inter alia, also dependent upon the thickness and type of the material to be knotted. Heretofore, the tension of the knotter needle was adjusted to the thickness and type of the material to be knotted by a more or less great curvature of the front end of the knotter needle. To this end, the knotter needle was bent manually and to the feel, which however, in addition to both a great experience and skilfulness, also requires repeated tests and each time dismantling of the knotter needle. Particular difficulties were encountered during the adjustment of the tension of the knotter needle in the processing of boucle yarn and effect yarn because in the case of these yarn types either the tension of the knotter needle was too great and then the loops present in the yarn were ravelled or the tension was too small and then the knot was not sufficiently firmly tightened.
The problem underlying this invention is to provide a knotting device of the above-mentioned type, which is particularly suitable for knotting boucle and effect yarn and which is adjustable in a simple and time-saving manner to the type and thickness of the threads to be knotted.
According to the invention, this problem is solved in that within the knotter mandrel there is provided a further needle (lifting needle) which is arranged for axial displacement and at its front free end has an inclined surface extending under an acute angle relative to the axial direction, in that the knotter needle underneath its hook is provided with a corresponding inclined surface cooperating with said inclined surface of said lifting needle, and in that control means are provided which shift the lifting needle at an adjustable moment in the direction of its free end against the knotter needle and thus lift the hook thereof from the inner wall of the knotter mandrel.
Hence the invention starts off from the idea of lifting the hook of the knotter needle from the inner wall of the knotter mandrel at an adjustable moment to thereby wholly or partially eliminate the clamping effect between the hook and the inner wall and thus to clear the thread ends or again to also decrease the counter-tension acting upon the thread ends. Since the moment at which the hook of the knotter needle is lifted from the inner wall of the knotter mandrel is exactly adjustable in the novel knotting device, it is possible to control the more or less firm tightening of the knot according to each respective material so that in the case of tender yarns a damage of the yarns, in particular a ravelling of the loops in boucle and effect yarns, will be avoided. Since the adjustment of the time at which the hook of the knotter needle is lifted from the inner wall of the knotter mandrel does not depend upon the bending of any members but merely upon the axial position of the lifting needle, this can be achieved in a simple manner by suitable mechanical adjusting means.